WATER SERVICES

Tundish and air gap requirements in Victoria

An air gap is a physical break between a discharge and the drain it falls into, and a tundish is the fitting that creates and shows it. Get rid of that gap with a direct connection and you have lost the protection the gap was there to give.

What an air gap is and why it matters

An air gap is an unbroken physical space between a discharge point and the highest level the wastewater below it could reach. Because nothing bridges that space, water cannot be drawn backwards from the drainage side into the line above. It is the simplest and most reliable form of backflow protection there is, and a tundish is how you build one into a relief or appliance drain.

Where a tundish or air gap is required

You will commonly see one called for on relief valve discharge lines, and on appliance connections such as a dishwasher or other equipment where wastewater must not be able to track back into the supply or the appliance. The principle is consistent: keep a visible break between the discharge and the drain. The exact situations and any dimensions sit in the current standard, so check it for the specific job rather than working from memory.

Common failures

• A relief drain connected straight into the waste, with no gap at all.
• The gap closed up later, by an extension piece or a fitting pushed up into it.
• A tundish set so low or so enclosed that the gap is effectively bridged.
• The discharge concealed, so a fault never gets seen.

What to photograph for the record

• The tundish in place, showing the clear gap below the discharge.
• The full run from the relief valve or appliance to the tundish.
• Where the drain terminates, showing it is safe and visible.

That set shows the gap is real and was not bridged, which is exactly what an inspector or insurer would want to see. Elemetric keeps that with the job.

Common questions

Why can't I directly connect a relief valve drain to the waste?

Because a direct connection removes the air gap. Without the gap, dirty water from the drainage side can be drawn back up the relief line under the wrong conditions, and a discharge is no longer visible. The break has to stay.

What does a tundish actually do?

It receives the discharge from a relief valve or an appliance, holds an air gap between that discharge and the drain below, and makes any flow visible so a fault gets noticed instead of running away unseen.

General information for licensed tradespeople, not legal or regulatory advice. The licensed plumber remains solely responsible for compliance. Refer to the current AS/NZS 3500 standards and the Building and Plumbing Commission (formerly the VBA) for authoritative requirements.